The Kashruth of Knives: An Amazing Mekori Perspective from Rav Yosef Qafih z”l

I have been studying the laws of kashrut as formulated by the Rambam in Hilkhot Ma’akhalot Assurot (Laws of Forbidden Foods) lately, and more in-depth than I ever have previously. Along the way, I have examined several elements of kashruth – particularly with regard to the status of kelim – that have bothered me for a while as either being unreasonable or illogical – i.e. out of step with visible and perceptible reality. One such subject is the kashrut of knives.

I have heard from various rabbis and mashgihim that knives which have been used to cut meat at any time, if they are used to cut an onion (a possible example of a davar harif – “sharp thing”) – EVEN IF THEY ARE CLEAN AND ARE COLD – the cut onion thereby “absorbs” the residue/taste of meat that are supposedly absorbed into the blade of the knife. As a result, according to those who maintain that this actually happens, the cut onion may thus not be eaten with dairy because it has now become “meaty.” This idea implies that there are invisible meat substances that we cannot perceive but are still there, and which present a problem halakhically. But as I reflected on this, it appears to fly in the face of other areas of kashrut where we rely on a principle of shalta be-`eina (“what is visible to the naked eye”). For instance, when it comes to insects on food, those which cannot be seen by the naked eye are halakhically insignificant, otherwise any microscope would no doubt reveal microscopic mites that feature on many things we are in daily contact with – even our own bodies. And if such a thing can be said about a bug – which is potentially forbidden de-oraitha – how can it not be said about supposedly invisible meat residue which is only forbidden de-rabbanan? I have suspected for a long time that there must be something lost in translation or a misunderstanding of Hazal in regard to knives.

My suspicions were delightfully confirmed upon reading the pirush of Rav Yosef Qafih (“Mori Yusef”) z”l on the Mishneh Torah. The following is my translation of a comment on Hilkhot Ma’akhalot Assurot 9:24. In it, Rav Qafih explains these laws from a sensible and reality-based perspective, one which brings the kashrut of knives and food cut by them back down to earth. Please note that all bolding, italics, bracketing, and underlining is for emphasis and is not in the original passage(s).


סכין שחתך בה בשר צלי וחזר וחתך בה צנון וכיוצא בו מדברים חריפין אסור לאוכלן בכותח אבל אם חתך בה קישות או אבטיח גורד מקום החתך ואוכל השאר בחלב

“A knife that was used to cut roasted meat, and it was then used again to cut ssenon [radish] – or things like it from the category of ‘sharp’ things – it is forbidden to eat them [i.e. the ssenon and similar things] with kutah [a thick dairy dip]. But if he used it afterward to cut kishut or avatiyah [types of melon], he scrapes the place where it was cut and he may then eat the rest with dairy.”


[30] In Hullin 111b, Hizkiyah says in the name of Abbaye, “Hilkhata [the final ruling is]… tzenon that one cut with a knife with which he cut meat – it is forbidden to eat it with kutah, and these things were said about tzenon since it, on account of its sharpness, will absorb, but with kishut he scrapes the place where it was cut and eats it [with kutah].” Behold, in the Gemara a knife used to cut roasted meat is not specifically mentioned, but only meat generally, and so it appears that Rabbenu [Rambam] is of the opinion that duhka (“pressing”) and harifuta (“sharpness”) never cause kelim to either give taste or absorb. And therefore, he adds “roasted meat” because by cutting roasted meat it will have lots of visible fat on it, and even though the following is not a formal proof of the matter, there is nevertheless an indication of this fact in what is brought in Beyssah 16a: “Rabbi Yisshaq says… the fat which is congealed on the surface of a knife, we scrape it off and rely on it for an eruv tavshilin.” And Rabbenu writes in Hilkhot Shevitat Yom Tov 6,4: “Even the fat that is congealed on the surface of the kind of knife that we use to cut roasted meat, it may be scraped together and if it contains the volume of an olive etc.” We see that according to Rabbenu a knife that we use to cut roasted meat usually has on it a thick layer of visibly congealed fat, such as that we can scrape from it an olive’s bulk. And therefore what is forbidden regarding ssenon is that, due to it’s sharpness, it will absorb the fat that is visible. This is not the case for something that is not sharp, since it merely wipes the fat off from the surface of the knife when it is cut and thus it is only necessary to scrape the fat from the place where it was cut. And in the printed edition, the redactors did not understand this emphasis of Rabbenu, namely that this halakhah deals specifically with a knife used to cut roasted meat, so they added the phrase “but if it was used to cut meat and then used again to cut kishut,” but this is not in the original handwritten manuscripts.

The Kesef Mishneh [written by Rav Yosef Qaro] writes here:

“In the chapter of Hullin entitled ‘Kol HaBasar‘ [page 112]: ‘Hizkiyah says in the name of Abbaye… ssenon that one cut with a knife with which he cut meat – it is forbidden to eat it with kutah, and these things were said about ssenon since it, on account of its sharpness, will absorb, but with kishut he scrapes the place where it was cut and eats it [with kutah]. Turnip stalks are permitted, but those of beets are forbidden. However, if he began by cutting a turnip and then proceeded to cut a beet stalk, then the beet stalks are permitted [to be eaten with kutah].’ And Rashi explains this passage as follows: ‘Even though it has been established for us that na”t bar na”t (i.e. transferred taste that is second-hand) is permitted, it is a different case to consider a knife that sometimes has congealed fat on it but is not recognizable as such. And when it cuts the tzenon, the na”t will come from the actual substance [i.e. it will be firsthand – na”t – and not second-hand – na”t bar na”t]. And further, due to its sharpness, it will absorb more that does boiled fish, and through the pressure exerted on the knife [duhka de-sakina], the knife will give taste and the tzenon will absorb it.’ And the Rashba writes: ‘The Rif did not write in the Halakhot regarding either turnip stalks or beet stalks, and neither did he include the statement that if one cut turnip stalks before he cut beet stalks, then the beet stalks [although sharp] are permitted [to be eaten with kutah]. Also the Rambam deleted it, and I have no idea why they both did so.’ And I maintain that Rabbenu, even though he did not write them explicitly, nevertheless they are included in his words in accordance with his explanation of the Gemara, for behold he wrote from ‘A knife that was used to cut roasted meat, and it was then used again…’ until ‘…he may then eat the rest with dairy.’ It appears that he is explaining that tzenon is lav davka [not specific, i.e. it could also something else similar to tzenon] since this is the rule for all sharp things, and it appears that he is also explaining that turnips are lav davka as well since this is the rule if one were to first cut bread or some other vegetable or fruit – because the prohibition to cut ssenon with such a knife is for no other reason than the congealed fat on its surface which strongly adheres to something sharp. So when that knife is first used to cut bread or any other thing, behold the knife is wiped clean thereby and no fat remains on its surface – so it is therefore permitted thereafter to cut tzenon with that knife. And now everything the Rabbenu states here is made clear, for from what he writes that ‘a knife that was used to cut roasted meat, and it was then used again to cut tzenon’ it is implied that what he means is: when a knife was used to cut the meat and then it was to cut ssenon without cutting anything else in between them and because of this lack of interruption it is forbidden. And since if he cuts something else between them it is thus permitted [!!!], there was no need for him to include the statement that ‘if he began by cutting a turnip and then proceeded to cut a beet stalk, then the beet stalks are permitted.’

And in regard to his statement that the knife was used to cut “roasted meat” being also lav davka since it is the same rule for meat that is either being cooked or boiled (however, there is room to say that he does specifically mean roasting meat like we said above because the fat of cooked meat is dissolved into the water and it does not congeal in a thick layer on the surface of the knife).  And he did not employ the phraseology of “meat” by itself in order to teach us that the cutting of boiled meat is what we are discussing here, but with regard to cold meat the fat does not congeal on the surface of the knife to the point that it would be forbidden to cut tzenon with it [!!!]. And it is not necessary to write about beets since they are included in what he writes “or things like it from the category of ‘sharp’ things.” And for this reason it is also not necessary to write “turnip stalks are permitted” since turnips are not in “the category of ‘sharp’ things.” And in this way it is possible to reconcile the summation of the Rif and it appears to me that it would be difficult to do so if their text of the Gemara was like ours, but it is already possible – even without this issue – that these words [i.e. regarding turnips and beet stalks] were not written in their versions of the Gemara [and therefore they did not write them down]…

This is nothing short of AMAZING! The implications of this beautiful and cogent explanation of the halakhah are apparent to anyone who is familiar with the traditional understanding of these laws. Basically, Rav Qafih is saying here that only visible, actual fat adhering to the blade is of halakhic concern – no invisible, lurking fat that is somehow [invisibly] “possessing” our kitchen cutlery to worry about!

Please let me know your thoughts and comments on this. This understanding completely revolutionized my understanding of kashruth in general and that of knives specifically.


5 thoughts on “The Kashruth of Knives: An Amazing Mekori Perspective from Rav Yosef Qafih z”l

    • Shalom, Alan. Thanks for replying. Le-`aniyyuth da`ati, this is speaking of a halakhically cold knife. Although he mentions “cold meat” in his comment, I think that Mori Yusef z”l may have been referring to uncooked or raw meat. But I could be wrong. I am still digging into all of the implications of this. However, should the knife in fact be halakhically hot (i.e. yadh soledeth bo), then it is treated like any other keli. So, if it was used like a skewer to roast meat (as was sometimes done anciently), then it requires libbun. And if it is used to cut hot food on the fire, then it is iruy keli rishon, etc. So, in regard to silverware, it seems that hot food – whether meat or dairy – requires a dedicated utensil, but cold (e.g. a meat spoon for cold cereal) is okay, but probably frowned upon. Hope that this helps.


  1. In the above you stated:

    ” And he did not employ the phraseology of “meat” by itself in order to teach us that the cutting of boiled meat is what we are discussing here, but with regard to cold meat the fat does not congeal on the surface of the knife to the point that it would be forbidden to cut ssenon with it [!!!]. ”

    I have two questions :

    [1] – With regard to either boiled, roasted, or cold meat, a modern steel knife will have fat on the surface. This fact can be demonstrated repeatedly so how did they come to this distinction?

    [2] – Regardless of which meat is cut with a knife or which vegetable, if one uses a modern detergent with mild warm or hot water, all fat or any traces of meat or vegetable will be removed with maybe the exception of onion or radish which may require more stringent cleaning. Nevertheless, it can be shown chemically that no fat remains regardless of the temperature of the meat. Does that change the picture? Obviously the Rabbis did not have this knowledge or advantage at the time to provide a perspective and it is unlikely that modern day Orthodox Rabbis would be very willing to change halachah concerning this approach. But it begs the question on the need for two sets of metal, e.g. stainless steel cutlery if one can be sure it is clean of all fat or “taste”. I would appreciate your thoughts about such an approach.

    It is interesting to see the Yemenite approach to the use of the knife. It is interesting that in contrast to most in Europe, and maybe in rest of Middle east, most Yemenites that I grew up with came with or used glass dishes exclusively for milk and meat as well as Pesach since glass does not retain “taste” and can simply be washed and then reused for another meal. I am sure there are those who chose to use ceramic-based dishes but in our community it was mostly the wealthy ones who could afford to have multiple sets of dishes. In our home, we used glass.


    • לק”י

      Shalom `alekha, David.

      Thank you very much for your comments and questions.

      First, let’s be clear that it was not me who authored the above quote, but Mori Yusef Qafih z”l. I only translated his comments from Hebrew. However, I think that I should be able to give satisfactory answers to your questions.

      [1] You are correct, a modern steel knife will have residue on it. This was true for knives manufactured in ancient times as well. The halakhah, however, does not seem to be concerned with residue, but actual shamen – the kind that can be be scraped off because it is congealed on the sides of the blade. Residue is the case with boiled or cold [likely raw], but roasted meat does not leave residue, it leaves a thick layer of congealed fat that, after sitting for a little while, resembles mayonnaise. It is this that the halakhah is concerned with. Residue occurs when cutting almost anything – even celery – but is usually halakhically insignificant since it usually does not transfer taste [ta`am] to the next thing cut. Another thing that must be kept in mind is that the halakhah, as stated in the Gemara and as communicated by the Kessef Mishnah above, specifically says that in order for one to be able to cut ssenon with a knife that cut meat, the knife must be used to cut something mild and parvah in between. As for simple residue, the Shulhan `Arukh deals with this questions specifically in Yoreh De`ah 96:4, and this passage is the source of the modern heter to purchase cut fruit from a non-kosher grocer. The reasoning, as stated by the Mehaber, is that the first cut removes any residue and then it is nullified many times over when all the cut fruit is gathered together [see there].

      (a) Again, you are correct that water and soap can sufficiently clean a knife in order for it to be used to cut something else. This is implied by the statement of cutting something mild and parvah after cutting meat before cutting something else in order to clean the knife. In other words, if bread or celery will clean the knife, kol she-ken (“all the more so”) will warm water and detergent clean it. In fact, the use of detergent has the added benefit that it nullifies any remaining meat residue, even if it remains on the knife since chemicals are generally regarded to be pogem eth ha-ta`am (“destroys the flavor”), and such “destroyed flavor” (ta`am nifgham) is considered halakhically insignificant. This is also why it is permissible to wash both meat and dairy dishes in the same sink – and even at the same time – as long as the water is not boiling and dish detergent is used.

      (b) And this brings me to my next point: chemical processes, microscopes, and residue swabs are NOT figured into halakhah. Therefore, whether fat can be detected chemically is 100% irrelevant to whether or not such fat particles are halakhically significant. The Torah, being a naturalistic legal system – i.e. needing little or no artificial instrumentation to determine a pesaq – its verities are determined by the naked senses alone. This means, chiefly, what the eye sees (i.e. shalta be-`eyna), what the ear hears (i.e. mashmia` ozen), and what the mouth tastes (i.e. akhilah and ta`am). This is also the reason, as stated by the ge’oniym, that Torah measured things in terms of eggs, olive, and other common agricultural measurements. So strong is the command to determine things by the senses rather than scientific means that even when Hazal were absolutely certain how to determine the calendar year within seconds of scientific accuracy when measured with instruments, they nevertheless declared it in accordance with the physical sighting of the new moon by witnesses. In fact, in the Gemara there is a recorded dispute between Rebbi Yehoshua` and the beyth diyn over which day should be the first day of Tishrey wherein in the nasiy of the beyth diyn explicitly goes with a less-compelling set of circumstances, based on a sighting by witnesses, over the scientific “calculation” [heshbon] of Rebbi Yehoshua` (cf. b.Rosh HaShanah 25a). The nasiy commanded him to appear before him with staff and money-bag on the day in which he reckoned it should be Yom HaKiypurriym (see there)! The reasons behind this principle are a bit complex and will have be left, perhaps, for another time.

      (c) You are incorrect, however, regarding the knowledge of the “ancient rabbis” regarding residues and even chemical processes. Archaeology and historical research shows that the ancients were at times more commonly versed in some of these things than we are today. The Talmudh discusses residue, fat, washing, soaps, etc. And as for modern-day rabbis “changing the halakhah,” I have good news: there is no need to “change” anything! Sefaradiy and Yemenite rabbaniym have held like this for many centuries, even until today. In fact, those that insist on adding unnecessary stringencies are the ones guilty of changing the halakhah since this was also the position of Hazal on the matter, as can be clearly seen from the Gemara in question.

      (d) We do not use two sets of knives or stainless steel cookware in our home. Most of our cookware is baking glass and Corelle, but the metal (stainless steel) pots used for boiling, etc. we use for both meat and dairy, washing them and scouring them in between. What we do separate are a couple of steel pans that we use for searing and broiling which become extremely dirty and do not come completely clean. We also separate plastic, but not silicone. My practical opinions on the matter are similar – although a bit more relaxed by comparison – as those expressed by Rav Yitzchak Abadi shlit”a of Jerusalem (see here). It should noted that when we cook for guests we use either foil pans or glassware, which is deemed acceptable by most everyone.

      [3] Nope, it was just Europe, and then only parts of Europe, who were so strict about glass. The Ra’avyah discusses the ubiquitous use of glassware and brings proofs for it in his halakhic compendium. He was an exact contemporary of the Rambam, only he was in France/Germany. Mainstream modern practice stems mainly from relatively late Hasidic influences on Ashkenaziy halakhic considerations and the comments of the Rema. The Jews of Spain (Iberia), Yemen, North Africa, and the Levant held similarly to what has been laid out here.

      Hope this is clear and has helped.

      All the best,

      Shabbath shalom,



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